When BP CEO Tony Hayward admits that “this is an environmental catastrophe” and President Obama proclaims from the Oval Office “already, this oil spill is the worst environmental disaster America has ever faced,” the gravity of the crisis cannot be denied. Eleven workers killed. Fishing industries shut down. Ecosystems under siege. All the while, oil continues to gush from an undersea well at a rate of up to two and a half million gallons a day. We are saddened and overwhelmed, but we are also curious about the science behind the Deepwater Horizon oil spill. What steps led to this catastrophe? How long will it last, and where do we go from here?
The Event: the explosion
From February-April 2010, the Deepwater Horizon, a mobile offshore drilling unit, was drilling a well 5,000 feet under the surface of the sea to access oil deposits in the Macondo Prospect. The rig was about 41 miles off the Louisiana coast in the Gulf of Mexico. Many oil deposits also contain methane, a major component of natural gas, and this flammable gas is a concern when drilling oil wells. On April 20th, 2010, a high-pressure stream of methane shot out of the drill column, causing explosions on the drilling rig, massive fires and the eventual sinking of the Deepwater Horizon. Eleven workers were killed in the explosion, and seventeen were injured.
Four days after the explosion, despite initial optimism, oil was confirmed to be leaking from the wellhead. Since then, the spill has become the largest oil spill ever to occur in US waters.
So what went wrong?
The oil deposit and drilling methods
Perhaps the biggest challenge in staunching the flow of oil and cleaning up the spill is the depth of the well site. While most offshore oil wells are located in relatively shallow waters, the Macondo wellhead is about a mile deep. Not only is the deep ocean location difficult to access and dark due to the low light penetration, but the increased pressure at such depths physically prevents much of the equipment from functioning properly. (At that depth, the pressure is about 150 times that of equipment on land!) Therefore, many of the methods and equipment engineered to manage situations like this are not applicable in the deep ocean.
To prevent explosions such as the one that occurred on the Deepwater Horizon, wellheads typically have what is called a “blowout preventer.” This device is deployed in the case of high pressure or out-of-control materials gushing from the well, and is designed to stop the flow until control can be restored. The blowout preventer failed at the Macondo well, perhaps due to a failed power supply and a damaged rubber sealing gasket.
Another component of the drilling and well equipment, the riser pipe, was damaged in the explosion. This riser pipe runs from the drilling equipment at the ocean surface down to the wellhead, and serves to guide and protect the drill and accompanying drilling fluids. When the explosion occurred, the riser pipe was badly damaged, and oil began to leak from several locations. Attempts to cap the well have been thwarted by the twisted and bent pipe, and while two of the main leakage sites have been capped, more than 75% of oil from the well may still be leaking into the Gulf.
Stopping the flow and clean-up methods
Many methods have been employed by BP thus far to attempt to limit the impact of the oil spill. The initial attempts were the most straightforward, focusing on stopping the leak at the failed blowout preventer. Remotely operated vehicles were sent underwater to manually close the valves on the preventer, but were all unsuccessful.
The next attempts focused on trying to essentially cap the damaged pipe –one such attempt was termed “top hat.” If the jagged, damaged riser pipe could be capped, the flow could be better contained and oil could be siphoned off. However, the first attempt to cap the pipe was foiled by crystals that form in the deep sea from a mixture of methane and water. These crystals caused the container to be more buoyant than was predicted and then clogged the system. While the top hat method did temporarily help to siphon the oil, it was ultimately removed in favor of attempts to stop the spill for good.
For a more reliable fix, the engineers then attempted what was termed “top kill.” The idea of this method was to pump heavy fluids into the blowout preventer to counter the pressure of the leaking oil and restrict the flow. The fluids used in drilling, called “muds”, have interesting flow properties, such as being either very fluid or very gel-like, depending on their movement. If the flow of oil was restricted, the pipe could then be sealed with cement and capped. However, this attempt also failed to restrict the flow as desired.
The most recent attempt, the Lower Marine Riser Package (LMRP) Cap Containment System, was designed to remove the damaged part of the riser pipe, thereby making the cap easier to fit and easier to siphon the oil onto a ship. A diamond-edged saw on an submersible robot was used to try to cut the pipe; however, the blade become stuck, forcing the use of a giant shears, making a jagged cut and making the capping more difficult. A second containment system is also now in place, and together with the well cap, possibly a third of the leaking oil is being captured.
Looking Ahead
There are a number of future options remaining. The most immediate option is to drill relief wells into the leaking well, thereby enabling the engineers to block the leaking well with drilling mud. These wells, however, will not be completed until August. Until then, a number of biological and chemical efforts are being made to reduce the environmental impact of the spill. In addition to human relief efforts, chemicals called dispersants are being used. Oil dispersants prevent clumping of oil and reduce environmental impact by acting as detergents, breaking up globs of oil into smaller pieces and allowing them to be carried by water. Another potential relief mechanism may come in the form of bioremediation – using bacteria to help “eat” the oil from the water. Some bacteria can feed off of oil, using it as a fuel source and helping to remove it from the water.
So what is our future? Despite great technological advances in recent decades, this disaster has proven so difficult to fix than even our best engineers have not discovered a way to adequately control the damage. Even after the leak has been stopped, scientists and engineers will be busy for years investigating the causes of the disaster and its long-term impacts. A detailed inspection of the blowout preventer, likely after it has been brought to the surface, will reveal why all of its many safeguards failed. The impacts of oil contamination on coastal habitats have been studied, but less is known about the influence of oil on deep ocean ecology. The prolonged release of this oil and the extensive use of dispersants will have effects on the ecosystem that we currently do not understand. The findings of both safety investigations and ecological studies may lead to new regulation of offshore drilling to prevent and contain future disasters.
Kevin Beier
Harvard Medical School
Links of interest:
New York Times interactive graphics: Methods attempted, blowout investigation, location of the oil, affects on wildlife:
http://www.nytimes.com/interactive/2010/05/25/us/20100525-topkill-diagram.html
Graphic of capping attempts:
http://media.nola.com/2010_gulf_oil_spill/photo/bp60210jpg-0287b162a5f1e30a.jpg
Timeline of events and other graphics from MSNBC:
http://www.msnbc.msn.com/id/36947751
Slideshow on “The physics of oil spills” from MSNBC:
http://www.msnbc.msn.com/id/37517080/ns/disaster_in_the_gulf
References:
Bluestein, Greg. (2010, May 25). BP engineers draw up plans for ‘top kill’. Associated Press. http://www.google.com/hostednews/ap/article/ALeqM5j2WM-6T8Nj9-NM50L97Qc8BdwyfgD9FU5PU00
Staff. (2010, June 4).”BP slices pipe in ‘significant step forward'”. MSNBC. http://www.msnbc.msn.com/id/37463005/ns/disaster_in_the_gulf/
Staff. “’Top kill’ BP operation to half US oil leak fails”. (2010, May 29). BBC News. http://news.bbc.co.uk/2/hi/world/us_and_canada/10191622.stm
Winning, David. (2010, May 3). “US Oil Spill Response Team: Plan To Deploy Dome In 6–8 Days”. The Wall Street Journal. http://online.wsj.com/article/BT-CO-20100503-700843.html
CBS Staff. (2010, May 16). “Blowout: The Deepwater Horizon Disaster: A Survivor Recalls His Harrowing Escape”. 60 Minutes. http://www.cbsnews.com/stories/2010/05/16/60minutes/main6490197_page2.shtml?tag=contentMain;contentBody
Mufson, Steven and Fahrenthold, David A. (2010, May 13). “Oil spill investigators find critical problems in blowout preventer.” Washington Post. http://www.washingtonpost.com/wp-dyn/content/article/2010/05/12/AR2010051202190.html?sid=ST2010051102889
Methane Hydrate Crystals Hamper Efforts to Contain BP Oil Spill. (2010, May 9). The Obligate Scientist. http://theobligatescientist.blogspot.com/2010/05/methane-hydrate-crystals-hamper-effort.html
Diamond, Patricia F. (2010, June 17). “Can Microbes Help Stem the BP Oil-Spill Disaster?”. Genetic Engineering and Biotechnology News. http://www.genengnews.com/analysis-and-insight/can-microbes-help-stem-the-bp-oil-spill-disaster/77899329/